I was responding to the OP's quote, it sounds like they might not be feeding their fish at all:
I was referring to the 'winter' temperatures, when I said, 'when in doubt I don't feed them.' I know that in cold weather they can't digest. Our weather has been all over the place, 20's one night, and a day or two later we are back in the 70s, back and forth and back. I'd just hate to feed them then find out it's going to freeze that night, I can't always get the weather, no tv or radio right now.
In the summer I usually feed them every day. There is a bunch of green / brown algae that I know they nibble on in there too. I also have plants around the 'pond' that atrract a bunch of bugs to the area, it's mostly under a tree (was only place I was allowed to put it) and there are often worm-thingys falling from the tree as well (I must wear a hat at all times, worms in hair - ew ew ew! lol), I think the fish eat these. I also catch some bugs to feed them - pretty much just have to scoop them off the plants around them lol.
I am a little worried about the sun they get though, they are under the shade till about 1pm - sundown, so they only get direct sunlight during the hottest part of the day (summer), if I add some plants that will shade the container, will the plants under the water get enough light?
(and do they get enough anyway?)
In a pond that small there isn't a lot of natural food available, I would never leave them entirely on their own. Platytudes now mentions feeding them 3-4 times a week and I think that is fine, but I wouldn't stop feeding them entirely in such a small space. I wouldn't recommend flakes either, I use a high quality small pellet food for my goldfish. It's not at all messy. And yes, it's unlikely that comets would spawn in a small pond, but they do for me each year in my larger pond.